1. Field of Invention
This invention pertains to controlled deceleration of a media handling mechanism during a power off condition, such as controlled deceleration of reels containing a media such as an information storage media.
2. Related Art and Other Considerations
Power-driven motors are often employed in the transport of media from a point of media supply to a point of media take-up. Such motors typically have media handling elements mounted to a drive shaft of the motor. One example of a media handling element is a reel about which the media is either wound or unwound. Abrupt termination of power to such motors during media transport can reak havoc unless deceleration of the transported media is controlled.
To the extent that prior art devices provide deceleration control, such control is generally implemented through mechanical braking of the media. Mechanical braking schemes consequentially involve additional mechanical components and are frequently ineffective.
To accurately control deceleration of media being fed to or taken up by a reel, numerous complex factors must be considered. Such factors include, at a minimum, the instantaneous speed of the media as well as the instantaneous radius of the media on the reel.
Unless such factors are properly considered, the media can experience inordinate tension during braking, which leads to media damage. In some instances, inaccurate braking (or no braking at all) may lead to erratic spooling of the media about the reel or even tape dumping. Erratic spooling and dumping typically require manual corrective intervention (with attendant delay) and, in aggravated cases, media damage.
Consideration of such factors would entail computation ability. However, during an abrupt power-off condition, the normal power supply is not available for powering any computational intelligence.
One example of a device for which controlled deceleration of media is paramount is a computer peripheral device known as a tape drive. A tape drive typically has magnetic recording tape extending between a tape supply reel and a tape take-up reel. Should power be disrupted to motors which actuate either reel, the foregoing problems can be experienced. In view of the sensitivity and delicacy of magnetic tape, and its importance for storing information, tape damage and tape mishandling cannot be tolerated.
One particular type of tape drive is a helical scan tape drive. Examples of helical scan tape drives are shown, inter alia, in the following US patents (all of which are incorporated herein by reference):
U.S. Pat. No. 4,835,628 to Hinz et al. PA1 U.S. Pat. No. 4,843,495 to Georgis et al. PA1 U.S. Pat. No. 5,065,261 to Hughes et al. PA1 U.S. Pat. No. 5,068,757 to Hughes et al. PA1 U.S. Pat. No. 5,142,422 to Zook et al.